The Ottoman Empire is a nation that occupies all of the Middle East, Turkey, Anatolia, and what used to be Iraq, or Persia. Its principal allies are its Muslim neighbors, Pakistan and the Mughal Empire, which is really a Republic with a titular Emperor.
The Caliph of Islam is the Sultan of the Empire, his titles are most frequently Amir ul Mumineen, Khalifa ul Islam, Imam ul Mumin. The Ottoman Branch is the most recent dynasty of the Caliphate, and the only one that has little to no opposition.
The Caliph's Palace in Istanbul near the Black Sea, which also serves as a Masjid.